It has long been known that wooden joists shrink across the grain thus causing the flooring to separate from the shoe strip and the door trim. The shrinking and warping of wooden joists causes plaster cracks and gives rise to sagging uneven floors, and this form of joist, though widely used in expensive as well as in low cost houses, has drawbacks.
Many prior proposals have been made aimed at the substitution of metal joists for the conventional wooden ones, but such metal joists which have been devised to meet the structural requirements of the various building codes, have generally been too expensive to manufacture in competition with wooden joists.
One of the features of metal structural members for residential construction to be used to the exclusion of wooden members, e.g. as joists and the like, is that they be nailable, so that flooring and sub-flooring can be easily secured to them. This has been a problem. Efforts to make the structural members, e.g. joists, nailable have often led to an undesired loss in strength. It is also important, of course, that the structural members be strong and capable of bearing loads and that they be relatively inexpensive.
Nailable metal structural members, e.g. for use as joists, have heretofore been proposed. Typical prior proposals are disclosed, for example, in Davis, et al., U.S. Pat. Nos. 2,578,465, and 3,164,227; in Goodwin, U.S. Pat. No. 2,605,867, and in Macomber, U.S. Pat. No. 2,630,890.
While these prior constructions are effective for their intended purpose, there is a continuing need for improved structures which are more easily and economically formed without sacrifice in strength and utility.